Project Abstract. This proposal requests funds to acquire an updated air handling unit (AHU) sized approximately 13,500 cfm to maintain proper temperature and air pressure differentials with humidity, building automation system, and exhaust fans replacing a >25 year old unit that is no longer serviceable for the Pathology vivarium at Colorado State University. The Pathology viviarium currently houses CSU's specific pathogen free (SPF) cat colony and a modest number of mouse cages used in prion research. This upgrade provides us the opportunity to vastly expand our housing capabilities and animal procedure space within our existing animal facilities. Specifically, the animal model core of the Prion Research Center (PRC) will be consolidated into the Pathology vivarium along with the SPF cat colony. The PRC currently has animals held in both the main animal holding facility, the Painter Center, and the Pathology vivarium. Over the past three years, the PRC has seen a 4-fold increase in animal census. This rapid growth has put constraints on the Painter Center holding capabilities. However, we have been reluctant to relocate animals to the available space in the Pathology vivarium due to mechanical concerns over the current air handling unit. There have been over 40 service calls the past two years to CSU Facilities Management to address concerns such as inability to maintain the appropriate temperature, inability to maintain appropriate airflow, and inability to maintain appropriate pressure differentials for biosecurity of the SPF cat colony and biocontainment for prion studies; and a mechanical assessment identified numerous concerns. Upgrading the AHU would provide stable environmental controls to appropriately house additional animals. Consolidating the PRC animal model core to the Pathology vivarium will more than double their existing housing and manipulation space. Furthermore, it will vacate space in the Painter Center which could be repurposed. There are currently only two procedure rooms outside of biocontainment for investigator use. By moving the prion users to the Pathology vivarium we can dedicate an additional three rooms to procedure space, as well as create additional animal holding space for current, new faculty recruits. This proposal will benefit all of the 53 principal investigators from12 academic departments with over $154M in current extramural grant support, including five faculty members from the PRC ($16.5M in current total funding). Because of the University's focus on infectious disease, cancer, and other biomedical research initiatives, this project will enhance a large portfolio of studies conducted to benefit animal and human health. Consistent with a strong record of support for development and maintenance of state of the art animal facilities, the Vice President for Research, the Dean of the College of Veterinary Medicine and Biomedical Sciences, the Chair of the Department of Microbiology, Immunology and Pathology have all enthusiastically supported this proposal. A modern AHU will also provide substantial energy savings. Construction will be managed with consideration for sustainable concepts directed by a LEED Accredited Facilities Professional Project Manager.